1. Field of the Invention
This invention relates to a composition usable as a primer for improving the adhesion of silicone compositions, especially silicone gels, to polymeric adherends.
2. Description of Related Art
Gels have been used for a variety of applications, such as sealing, encapsulation, acoustic isolation or damping, insulation, and the like. Properties which make gels valuable in such applications include their conformability, adhesion to a wide variety of materials, and re-enterability. Typically, a gel is a high elongation, low modulus (soft) material. A preferred type of gel is a silicone gel.
Generally, gels have satisfactory adhesive strength to most adherends with which they come in contact. However, for certain polymers, such as polyphenylene oxide, polycarbonate, ABS/polycarbonate alloy, and polypropylene, it may be necessary or desirable to improve adhesion by employing a primer. (These polymers may be used for molded parts such as electrical connectors and terminations, which are then filled with silicone gel to provide environmental sealing around electrical connections within the part.) Illustrative disclosures relating to gel-containing electrical articles include Debbaut, U.S. Pat. No. 4,600,261 (1986); Debbaut, U.S. Pat. No. 4,634,207 (1987); Uken et al., U.S. Pat. No. 4,643,924 (1987); Uken et al., U.S. Pat. No. 4,662,692 (1987); Debruycker et al., U.S. Pat. No. 4,846,721 (1989); Shimirak et al., U.S. Pat. No. 5,069,636 (1991); Mattis et al., U.S. Pat. No. 5,153,988 (1992); Pinyan et al., U.S. Pat. No. 5,167,526 (1992); Mattis et al., U.S. Pat. No. 5,273,449 (1993); Roney et al., U.S. Pat. No. 5,347,084 (1994); Shimirak et al., U.S. Pat. No. 5,449,299 (1995); Shimirak et al., U.S. Pat. No. 5,601,460 (1997); and Huynh-Ba et al., U.S. Pat. No. 5,828,005 (1998).
We have found a commercially available primer which is technically suitable for polyphenylene oxide, but which is less effective with ABS/polycarbonate alloy and not effective at all with polypropylene. Further, the use of this primer is commercially undesirable because it is very costly and also because it contains as a carrier VMandP (varnish makers"" and painters"") naphtha, which is very flammable (flash point 40xc2x0 F.) and somewhat toxic. Because of these hazardous properties, processing of the waste stream from manufacturing operations using this primer can be expensive.
In view of the foregoing, it is desirable to develop a primer for silicone gels which is superior to prior art primers in one or more of the foregoing respects, in particular being efficacious with a variety of polymers, having reduced flammability, and/or having reduced toxicity.
We provide a composition comprising:
(a) between 0.125 and 2.5 weight percent of a first coupling agent which is
(i) a titanium containing coupling agent selected from the group consisting of tetra-2-ethylhexyl titanate, tetra-n-butyl titanate, tetracresyl titanate, and tetramethoxypropoxy titanate;
(ii) a boron-containing coupling agent selected from the group consisting of trimethoxyboroxine, triphenoxyboroxine, triphenyl borate, and tris(trimethylsiloxy) boron;
(iii) a zirconium-containing coupling agent selected from the group consisting of zirconium tetra-2-ethylhexanoate, tetraphenoxy zirconate and tetra-2-ethylhexyl zirconate; or
(iv) a combination of the aforesaid titanium-, boron-, and zirconium-containing coupling agents;
(b) between 0.125 and 2.5 weight percent of a second coupling agent which is a silane coupling agent selected from the group consisting of tris(3-(trimethoxysilyl)propyl)isocyanurate and N-phenyl-xcex3-aminopropyl-trimethoxysilane; and
(c) between 99.75 and 95.0 weight percent of a carrier solvent; the weight percent""s being based on the combined weights of first and second coupling agent and carrier solvent.
In another aspect of the invention, we provide a method of bonding a crosslinked silicone composition to a polymer surface, comprising the steps of:
(I) providing an article having a polymer surface to which a crosslinked silicone resin is to be adhesively bonded;
(II) coating the polymer surface with a composition comprising
(a) between 0.125 and 2.5 weight percent of a first coupling agent which is
(i) a titanium containing coupling agent selected from the group consisting of tetra-2-ethylhexyl titanate, tetra-n-butyl titanate, tetracresyl titanate, and tetramethoxypropoxy titanate;
(ii) a boron-containing coupling agent selected from the group consisting of trimethoxyboroxine, triphenoxyboroxine, triphenyl borate, and tris(trimethylsiloxy)boron;
(iii) a zirconium-containing coupling agent selected from the group consisting of zirconium tetra-2-ethylhexanoate, tetraphenoxy zirconate and tetra-ethylhexyl zirconate; or
(iv) a combination of the aforesaid titanium-, boron-, and zirconium-containing coupling agents;
(b) between 0.125 and 2.5 weight percent of a second coupling agent which is a silane coupling agent selected from the group consisting of tris(3-(trimethoxysilyl)propyl)isocyanurate and N-phenyl-xcex3-aminopropyltrimethoxysilane; and
(c) between 99.75 and 95.0 weight percent of a carrier solvent; the weight percent""s being based on the combined weights of first and second coupling agent and carrier solvent;
(III) drying the composition;
(IV) applying onto the polymer surface an uncrosslinked silicone composition; and
(V) crosslinking the silicone composition to form an adhesive bond between crosslinked silicone composition and the polymer surface.